北京“7.21”特大暴雨云降水结构及云雨转化特征

Characteristics and transformation of cloud and precipitation of the extreme torrential rain in Beijing on 21 July 2012

摘要:

利用多普勒雷达资料、FY-2E静止卫星和MODIS极轨卫星反演产品,研究2012年7月21日北京特大暴雨的云降水结构及云雨转化特征。结果表明:降水过程三阶段的云降水垂直结构不同。1)在暖区对流降水阶段,降水以暖雨机制启动,雨滴在暖区存在深厚的碰并增长过程,暖雨过程对降水起主要贡献。随着云体的发展,冷雨过程加剧。T-R_e分析表明,-10 ℃层以下云滴凝结碰并显著,-10 ℃层以上为深厚的冰相增长带,云顶以冰相大粒子为主,云水向雨水转化迅速。2)在锋面对流降水阶段,降水系统为高度组织化的“低质心”强降水液态MCC(Mesoscale Convective Complex)系统。回波强度在冰水混合层增长较快,冻结层是此阶段成雨微物理的关键层。降水粒子在暖云区碰并增长较快,而蒸发或破碎过程并不显著。3)在锋后降水阶段,0 ℃层附近冰晶粒子与云水的碰并增长较为明显。前期降水存在明显的雨滴蒸发过程。随着云体的发展,暖区云水含量较少,降水粒子不能有效碰并增长。

关键词:特大暴雨;云降水结构特征;多普勒雷达;卫星反演云参数

Abstract:

Using the data of Doppler radar and the cloud paramters products retrieved from FY-2E geostationary satellite data and MODIS Polar-orbiting satellite data,this paper analyzes the structure and transformation of cloud and precipitation in the extreme torrential rain process in Beijing on 21 July 2012.It shows that three stages of the precipitation process have different vertical structures of cloud and precipitation.1)In the warm area convective precipitation stage,the precipitation starts with the warm rain process.The rain drops grow quickly with significant coagulation in the warm cloud area,and the warm rain process is important for precipitation.With the development of cloud,the cold rain process is intensified.T-Re analysis shows that cloud droplets grow quickly below -10 ℃ level with significant condensation-coagulation.There is a deep zone of mixed phase above -10 ℃ level,with the top of cloud dominated by ice particles,and cloud water converts to rainfall quickly.2)In the front convective precipitation stage,the liquid MCC(Mesoscale Convective Complex) system with highly organization and low centroid is the main precipitation system with high rainfall intensity.The echo intensity increases quickly at ice-water mixed layer,and the freezing layer is the key area of rain microphysical process.The rain drops grow quickly with significant coagulation in the warm cloud area,but the broken or evaporation is not obvious.3)In the backward front precipitation stage,the ice particles increase quickly at near 0 ℃ level by coagulating cloud water.There is obvious evaporation in the early precipitation process.With the development of cloud,cloud water is less in the warm cloud area,and the rain drops can not grow without effective coagulation.

Key words:extreme torrential rain;characteristics of cloud and precipitation;Doppler radar;cloud parameters retrieved from satellite data